luci-mod-network: spelling / grammar

luci-mod-network: spelling / grammar

"Setup" is a noun, the thing. "Set up" is a verbal idiom, the action.

One cannot setup a DHCP server, just as one cannot fuckup a test, or
ripup some paper. One can, however, set a DHCP server up, and one can
fuck a test up, and rip some paper up.

Signed-off-by: Paul Dee <systemcrash@users.noreply.github.com>